A system for sound recording and playback is known which is termed “stereophonic system” and consists in acquiring a sound by means of two or more microphones, arranged in suitable positions with respect to the sound source, which convert the sound into a plurality of electrical signals, which are then sent to a suitable amplifying and/or recording device, which is adapted to amplify and record and/or process appropriately the signals, thus producing two additional distinct signals which can be sent respectively to two distinct speakers; by positioning the speakers appropriately, it is possible to obtain the sensation of a sound which partially reproduces the three-dimensionality of the real sound.
However, this known type of recording system has drawbacks: in fact, the played back sound is not received in a fully three-dimensional manner, and at best it is possible to obtain a sensation of right or left displacement of the sound, whose correspondence to the real sound depends on the mutual position of the speakers and of the listener.
This known type of sound recording and playback system is therefore inadequate to play back realistically the effect of a sound source which moves, for example, around and/or above the listener.
Sound recording and playback systems are also known which are referenced by the DOLBY SURROUND trademark and provide for the editing, on the part of a sound engineer, of prerecorded audio signals which are then divided, with the aid of an appropriately provided electronic device, such as for example a mixer and/or a computer, into a plurality of multiple channels (typically five or seven, plus an additional channel for the lower frequencies), which are intended to be sent to separate speakers arranged appropriately, typically proximate to the corners of the room where they are used and in front of the listener.
This known type of sound recording and playback system also allows to reproduce the effect of a sound source which moves around the user, with the limitation that this movement always occurs on a horizontal plane.
Therefore, even this known type of sound recording and playback system has drawbacks: in addition to not allowing to transmit to the listener the sensation of a sound source that moves above him, in order to obtain the sensation of the movement of the sound source around the listener it is necessary to have at least five speakers, and therefore this sensation cannot be obtained with listening devices of the portable type which use headphones or earpieces.
Moreover, to achieve a good result during sound playback, the room in which the speakers are arranged must have a square or rectangular plan shape, and this limits the possible applications of this known type of system.
Another drawback of this known type of recording and playback system is that it entails high costs, which can be due both to the step for editing the audio track and to the sound playback step; editing the audio track in fact requires the work of specialized personnel and the use of suitable electronic and/or software devices, which are often very expensive, whereas sound playback requires the use of an appropriately provided playback system, equipped with suitable outputs and with a plurality of speakers, whose cost can be high.
In order to try to optimize the recording of a sound, particularly to listen to it with earpieces, playing back as faithfully as possible the perceptions of a listener located in the room where the sound source is located, a recording technique known as binaural is used which employs a support which has the shape and dimensions of a stylized human head and is made of a material which is adapted to reproduce as much as possible the sound absorption of an actual human head.
This support reproduces faithfully in particular the shape of the auricles and of the auditory canals; two high-fidelity microphone cartridges are fixed respectively to the internal end of the auditory canals and therefore pick up sound in a manner which is similar to the manner in which the eardrum of a listener whose head were arranged like the support would perceive it.
This known type of recording technique also has drawbacks, however; first of all, to achieve good results during playback it is necessary to use very high-quality headphones, which are very expensive.
Further, this known type of technique is inadequate in the reproduction of sounds generated by sources arranged in front of the listener, and the perception of the three-dimensionality of sound is further limited.
Moreover, the sound perceived by the listener during playback cannot be traced back to the sound that reaches the microphone cartridges during recording, since such cartridges record the sound as it would reach the eardrums, while the sound source for the listener is constituted by the earpieces, which are arranged at the auricle of the listener, in contact with the outlet of the auditory canals.